This invention relates generally to pressure measuring apparatus, and has particular reference to a novel construction for a blood pressure measuring device or sphygmomanometer, which construction results in an efficient and very accurate instrument.
A relatively large number of blood pressure measuring devices have been developed over the years with some very advantageous designs having been provided. A problem with even some of the best designs, however, has been that of achieving and maintaining accurate calibration, including precise zero settings for indicator gauges. This means that if in a periodic test an instrument is found to be inaccurate it must be returned to the factory for recalibration which obviously is an inconvenience. Other problems that have occurred in prior art devices involve obtaining satisfactory bleed valve performance and achieving fluid tight integrity within the device.
The closest prior art known to the applicants is disclosed in U.S. Pat. Nos. 3,738,357, issued June 12, 1973 to Roger Hayes; 3,823,707, issued July 16, 1974 to Roger Hayes; 4,013,265, issued Mar 22, 1977 to B. Speidel and 4,243,201, issued Jan. 6, 1981 to B. Speidel. These patents are chiefly directed to bleed valve performance and do not disclose a piston and rolling diaphragm assembly, as taught by the present invention, for moving the gauge needle in response to fluid pressure in the blood pressure cuff. The cited prior art also lacks externally accessible calibration adjustments as disclosed herein which adjustments enable the physician to maintain accurate calibration in his blood pressure measuring device without the need to return it to the factory. Other differences between the construction of the device of the invention and those of the prior art will become apparent as the description proceeds.